The aim of this study is to present a theoretical study of a silicon solar cell under frequency modulation. Solving the continuity equation lead to the analytical expressions of the minority carriers’ density, the photocurrent and the photo voltage. The photocurrent and the photo voltage are plotted versus the modulation frequency in a semi-logarithmic scale for various incidence angles; the dynamic impedance of the solar cell is then derived. The Nyquist diagram of the impedance is plotted for various incidence angles, leading to the determination of the series and parallel resistances. The determination of the diffusion capacitance is also made based on the Bode diagram of the solar cell impedance. The influence of the modulation frequency and the incidence angle on the diffusion capacitance and the series and parallel resistances is then exhibited.